hojbot tz command

tz.txt

Improve tz command
- "tz me <my-time-zone>" command to configure per-user time zone
- "tz alias add <alias> <zone-name>" command to add system aliases
- "tz alias rm <alias>" command to remove system aliases
- target time zone command "tz <date> <time> <zone1> to <zone2>,<zone3>,..."
  (without zone2+, it converts to user's own time zone, or direct user to use tz me command)

Reference: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

Examples:

> tz me America/Los_Angeles
@tk3369, your time zone preference is now America/Los_Angeles.

> tz me America/wat
@tk3369, sorry, time zone "America/wat" is not valid. 
You can find a list of time zones at https://en.wikipedia.org/wiki/List_of_tz_database_time_zones


> tz alias list
@tk3369, time zone aliases are as follows:
- LA: America/Los_Angeles
- BRU: Europe/Brussels

> tz alias add NY America/New_York
@tk3369, time zone alias "NY" has been set to "America/New_York"

> tz alias rm NY 
@tk3369, time zone alias "NY" has been removed.

> tz alias rm BMW
@tk3369, sorry, time zone alias "BMW" does not exist.

> tz 2021-03-21 03:00PM LA to NY
@tk3369, 2021-03-21 03:00PM LA = 2021-03-21 06:00PM NY

> tz 2021-03-21 03:00PM LA to BMW
@tk3369, sorry, time zone "BMW" does not exist.